Re: [RESEND PATCH v5 0/7] gpiolib: add an ioctl() for monitoring line status changes

[Andy Shevchenko <andriy.shevchenko@xxxxxxxxxxxxxxx>]

On Thu, Jan 23, 2020 at 03:04:59PM +0100, Bartosz Golaszewski wrote:
> From: Bartosz Golaszewski <bgolaszewski@xxxxxxxxxxxx>
> 
> Resending with some people who could ack kfifo patches in copy.

Haven't you got Ack from Stefani [1]?

[1]: https://lkml.org/lkml/2020/1/7/514

> 
> ===
> 
> When discussing the recent user-space changes with Kent and while working
> on dbus API for libgpiod I noticed that we really don't have any way of
> keeping the line info synchronized between the kernel and user-space
> processes. We can of course periodically re-read the line information or
> even do it every time we want to read a property but this isn't optimal.
> 
> This series adds a new ioctl() that allows user-space to set up a watch on
> the GPIO chardev file-descriptor which can then be polled for events
> emitted by the kernel when the line is requested, released or its status
> changed. This of course doesn't require the line to be requested. Multiple
> user-space processes can watch the same lines.
> 
> This series also includes a variety of minor tweaks & fixes for problems
> discovered during development. For instance it addresses a race-condition
> in current line event fifo.
> 
> First two patches add new helpers to kfifo, that are used in the later
> parts of the series.
> 
> v1: https://lkml.org/lkml/2019/11/27/327
> 
> v1 -> v2:
> - rework the main patch of the series: re-use the existing file-descriptor
>   associated with an open character device
> - add a patch adding a debug message when the line event kfifo is full and
>   we're discarding another event
> - rework the locking mechanism for lineevent kfifo: reuse the spinlock
>   from the waitqueue structure
> - other minor changes
> 
> v2 -> v3:
> - added patches providing new implementation for some kfifo macros
> - fixed a regression in the patch reworking the line event fifo: reading
>   multiple events is now still possible
> - reworked the structure for new ioctl: it's now padded such that there
>   be no alignment issues if running a 64-bit kernel on 32-bit userspace
> - fixed a bug where one process could disable the status watch of another
> - use kstrtoul() instead of atoi() in gpio-watch for string validation
> 
> v3 -> v4:
> - removed a binary file checked in by mistake
> - drop __func__ from debug messages
> - restructure the code in the notifier call
> - add comments about the alignment of the new uAPI structure
> - remove a stray new line that doesn't belong in this series
> - tested the series on 32-bit user-space with 64-bit kernel
> 
> v4 -> v5:
> - dropped patches already merged upstream
> - collected review tags
> 
> Bartosz Golaszewski (7):
>   kfifo: provide noirqsave variants of spinlocked in and out helpers
>   kfifo: provide kfifo_is_empty_spinlocked()
>   gpiolib: rework the locking mechanism for lineevent kfifo
>   gpiolib: emit a debug message when adding events to a full kfifo
>   gpiolib: provide a dedicated function for setting lineinfo
>   gpiolib: add new ioctl() for monitoring changes in line info
>   tools: gpio: implement gpio-watch
> 
>  drivers/gpio/gpiolib.c    | 351 +++++++++++++++++++++++++++++---------
>  drivers/gpio/gpiolib.h    |   1 +
>  include/linux/kfifo.h     |  73 ++++++++
>  include/uapi/linux/gpio.h |  30 ++++
>  tools/gpio/.gitignore     |   1 +
>  tools/gpio/Build          |   1 +
>  tools/gpio/Makefile       |  11 +-
>  tools/gpio/gpio-watch.c   |  99 +++++++++++
>  8 files changed, 486 insertions(+), 81 deletions(-)
>  create mode 100644 tools/gpio/gpio-watch.c
> 
> -- 
> 2.23.0
> 

-- 
With Best Regards,
Andy Shevchenko